1. Field of the Invention
The present invention relates to an apparatus and method for detecting additional data which is embodied in compressed-motion image data.
2. Description of the Related Art
The MPEG (Moving Picture Experts Group) standard is known as a set of rules for motion image data compression. In accordance with the MPEG rules specified in ISO (International Organization for Standardization), data is compressed by (1) resolving the frequency of input image data frame by frame using a DCT (Discrete Cosine Transform) technique so as to generate DCT coefficients, and (2) quantizing the generated DCT coefficients while paying no attention to high-frequency components of the resolved frequency. Particularly, pictures of original image data are re-grouped into a GOP (Group Of Pictures) including three types of pictures, xe2x80x9cIxe2x80x9d picture, xe2x80x9cPxe2x80x9d picture and xe2x80x9cBxe2x80x9d picture. A header (SH: Sequence Header) is attached to the GOP, and the GOP with the attached header is transmitted, recorded and reproduced as compressed motion image data. The xe2x80x9cIxe2x80x9d picture is an Intraframe-Picture, which is encoded within one frame based only on pixel data. The xe2x80x9cPxe2x80x9d picture is a predictive-interframe picture which is encoded based only on forward directional prediction between frames with a past reference. The xe2x80x9cBxe2x80x9d frame is a bi-directional picture, which is encoded based on bi-directional predeiction between frames with a past and future references. Predictive encoding is performed with a code, which is DCT (Discrete Cosine Transform) coded based on an error in successive frames, and a motion vector.
There are, thus, great demands for a technique for embodying additional data, such as a signal for preventing reproduction of data, into MPEG data as compressed-motion image data, and a technique for detecting such additional data. It is advantageous, in terms of the processing speed, that such additional data can be detected without performing DCT transformation for the MPEG data.
The above technique for detecting the additional data without performing the DCT transformation is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-74794. In the technique disclosed in the publication, additional data is a spread-spectrum signal, and is embodied in serial components of DCT spectrums of original image data An additional data detection circuit extracts the serial components, performs inverse spreading processing, and acquires additional data without performing inverse DCT transformation for the DCT spectrums of the original image data.
In this prior-art technique, it is necessary to detect whether additional data or what additional data is embodied throughout the entire pictures of a GOP of the MPEG data. Therefore, it is very time-consuming to detect the presence of additional data or the contents of additional data. When to reproduce pictures of image data in rapid motion, the image data is undesirably deteriorated. In the case where additional data is attached only to some pictures within one GOP, instead of being attached to the entire pictures, it is no use detecting the entire pictures.
It is accordingly an object of the present invention to provide an apparatus and method for detecting additional data added to compressed-image data at speed.
Another object thereof is to provide an apparatus and method for detecting additional data added to compressed-image data with high efficiency.
In order to achieve the above object, according to the first aspect of the present invention, there is provided an additional data detection system comprising:
an analyzer which receives and analyzes compressed-image data, extracts and outputs image data of a predetermined image, and also outputs image ID (identification) information regarding the analyzed image data;
a degree-of-coincidence determinator which determines a degree of coincidence of the image data output by the analyzer and image data of an image including pre-set additional data, and outputs a signal representing presence of additional data when the determined degree of coincidence is equal to or greater than a predetermined reference value; and
a setting unit which receives the degree of coincidence output by the degree-of-coincidence determinator and the image ID information output by the analyzer, obtains a correlation between the image ID information and the degree of coincidence, specifies image ID information of an image which is estimated to have a predetermined degree of coincidence, and operates the degree-of-coincidence determinator to determine a degree of coincidence of image data at a timing the specified image ID information is output from the analyzer.
According to this structure, the setting unit determines the image ID information of an image which is estimated to have a predetermined high degree of coincidence, based on the image ID information and the degree of coincidence, and operates the additional data detector at a timing the image ID information is output. The additional data detector can detect additional data with high efficiency, because it needs to carry out only a process for detecting image data which is estimated to have a quite high degree of coincidence.